Is Topguard the Best Fungicide for Frogeye Leaf Spot in Soybeans?

Frogeye leaf spot (FLS), a foliar fungal disease caused by the Cercospora sojina, can be a costly problem for soybean growers. Symptoms of the disease are commonly recognized during R stages. Topguard, which has the active ingredient flutriafol, is one of the top treatments among fungicide options, but there are several factors to keep in mind.

Understanding Efficacy Ratings

When choosing between fungicides, check for relevant efficacy ratings. In this particular case, a chart like this would help: “Fungicide Efficacy for Control of Soybean Foliar Diseases.”

For controlling frogeye leaf spot, Topguard 1.04SC® (flutriafol 11.8%) and Topguard EQ 4.29SC® (azoxystrobin 25.3% and flutriafol 18.63%) are both rated as G-VG, meaning good to very good.

Other fungicides rated as very good for treating frogeye leaf spot in soybeans include Topsin-M® (thiophanate-methyl), Quadris Top 2.72SC® (azoxystrobin 18.2% and difenoconazole 11.4%), Lucento 4.17SC® (flutriafol 26.47% and bixafen 15.5%), Miravis® Neo (pydiflumetofen 7.0%, azoxystrobin 9.3%, and propiconazole 11.6%), and Acropolis® (thiophanate-methyl 21.3% and tetraconazole 4.2%).

Treating Multiple Diseases

If your crop scouting efforts have revealed multiple diseases in your soybean fields that need to be controlled with fungicides, then it’s important to consider what treatment options can best handle the multi-faceted protection your crops need. For example, Topguard 1.04SC® is very good at treating anthracnose, but poor with target spot.

Another factor to consider is your crop rotation in general. For example, “Topguard fungicide provides residual protection in a variety of crops including corn, soybeans, peanuts, sugar beets, cotton, wheat, triticale, tree nuts, cucurbits and fruiting vegetables.” Hence, what else you grow throughout the year can affect what fungicide is best to apply to your current soybeans.

Avoiding Resistance

Spraying the same fungicide multiple times in the same growing season and year after year is a recipe for disaster when it comes to fungicide resistance. Growers should rotate which products to apply and, when possible, choose a mixed mode of action.

FMC Corporation, who makes Topguard products, is quick to explain: “Topguard® EQ fungicide . . . is the only premix that combines the benefits of highly systemic and long-lasting Group 3 fungicide, flutriafol, with a best-in-class Group 11 strobilurin fungicide azoxystrobin. This unique combination broadens the spectrum of diseases that can be controlled and offers two modes of action to combat disease resistance.”

Paying Attention to Timing

Treating FLS with fungicides is generally most effective when applications are made during the R3-R5 growth stages. There are also harvest restrictions to be aware of. For example, Topguard 1.04SC® and Topguard EQ 4.29SC® both have a grain-related harvest restriction of 21 days.